Arc discharge lamp control circuit

ABSTRACT

A high-frequency, lightweight, solid-state ac ballast for operating arc discharge lamps such as fluorescent lamps. An ac ballast in accordance with the invention includes a single transistor and a storage capacitor interconnected with a lightweight air-gap ferrite core transformer provide a blocking oscillator circuit capable of high-frequency ac operation. To initiate operation of the blocking oscillator circuit, lowfrequency (e.g., 50-60 hertz) ac input voltage signals are converted to a dc voltage and applied to a starting circuit for producing a voltage for charging the storage capacitor. When the voltage developed across the capacitor reaches a predetermined value, the transistor is forward biased into conduction thereby initiating operation of the blocking oscillator circuit. After a predetermined period of time, the transistor is reversed biased by a voltage produced across a regenerative feedback winding of the air-gap transformer thereby terminating operation of the blocking oscillator circuit. During the operation of the blocking oscillator circuit through several cycles, high-frequency ac voltage signals (e.g., 20 kilohertz) are produced across a load winding of the air-gap transformer for operating a pair of fluorescent lamps. A modified version of the abovedescribed ac ballast includes a square hysteresis loop ferrite toroid in the blocking oscillator circuit, in addition to the air-gap transformer, for causing the transistor to switch more quickly between its conducting and nonconducting states.

United States Patent Cluett 51 Oct. 24, 1972 [54] ARC DISCHARGE LAMP CONTROL CIRCUIT [72] inventor: Ronald D. Cluett, Gloucester, Mass.

[73] Assignee: GTE Laboratories Incorporated [22] Filed: Jan. 4, 1971 [21] Appl. No.: 103,582

[52] US. Cl. ..315/101, 315/98, 231/112 [51] Int. Cl. "11051) 41/29 [58] Field OISearch ..315/101, 108, 98

[56] References Cited UNITED STATES PATENTS 3,008,068 11/1961 wilting et al. ..315/206 3,389,299 6/1968 Bell ..315/206 2,923,856 2/1960 Greene ..315/138 3,457,458 7/1969 Paget ..315/284 3,034,015 5/1962 Schultz ..315/97 2,964,676 12/1960 Davies et al. ..315/98 Primary Examiner-Herman Karl Saalbach Assistant Examiner-C. Baraff AttorneyElmer J. Nealon, Peter Xiarhos and Irving M. Krugsman ABSTRACT A high-frequency, lightweight, solid-state ac ballast for Ann operating arc discharge lamps such as fluorescent lamps. An ac ballast in accordance with the invention includes a single transistor and a storage capacitor interconnected with a lightweight air-gap ferrite core transformer provide a blocking oscillator circuit capable of high-frequency ac operation. To initiate operation of the blocking oscillator circuit, low-frequency (e.g., 50-60 hertz) ac input voltage signals are converted to a dc voltage and applied to a starting circuit for producing a voltage for charging the storage capacitor. When the voltage developed across the capacitor reaches a predetermined value, the transistor is forward biased into conduction thereby initiating operation of the blocking oscillator circuit. After a predetermined period of time, the transistor is reversed biased by a voltage produced across a regenerative feedback winding of the air-gap transformer thereby terminating operation of the blocking oscillator circuit. During the operation of the blocking oscillator circuit through several cycles, high-frequency ac voltage signals (e.g., 20 kilohertz) are produced across a load winding of the air-gap transformer for operating a pair of fluorescent lamps.

A modified version of the abovedescribed ac ballast includes a square hysteresis loop ferrite toroid in the blocking oscillator circuit, in addition to the air-gap transformer, for causing the transistor to switch more quickly between its conducting and non-conducting states.

SCIaInmZDraMngfigures PATENTEB um 24 um SHEU 1 BF 2 FIG.|

1 ARC DISCHARGE LAMP CONTROL CIRCUIT BACKGROUND OF THE INVENTION The present invention relates to a control circuit for operating arc discharge lamps and, more particularly, to a single-transistor solid-state ac ballast for operating arc discharge lamps such as fluorescent lamps.

The use of ac ballasts for operating arc discharge lamps such as fluorescent lamps is well known to those skilled in the art. For example, it is commonly known to employ an inductive transformer ballast to supply a high starting voltage to one or more fluorescent lamps to ionize the gas in the lamps and thereby to start discharge and also to limit the current through the ionized lamps to a predetermined rated value. Although inductive transfonner ballasts are presently the most common type of ballasts used in fluorescent lighting applications, particularly in high-power lighting applications, they nonetheless tend to be heavy and bulky, due to the large amounts of copper winding and iron employed by the transformers in such ballasts, thereby resulting in an undesirably high cost. In addition, such ballasts produce large amounts of unwanted heat and noise. Moreover, such ballasts are capable of only low-frequency operation, e.g., 50-60 hertz, thereby resulting in lamp operating efiiciency which is less than optimum.

To overcome some of the problem associated with the above described inductive transformer ballasts, particularly weight problems, it has been proposed to replace such ballasts with inductive ballast arrangements including relatively lightweight transfonners such as autotransformers. The control of the operation of these autotransformers to produce the desired mode of operation of a fluorescent lamp load is achieved by pulse generating, gating, or switching circuits interconnected with the autotransformers. Typically, these circuits include solid-state devices such as silicon controlled rectifiers, Diacs, and Triacs. While the abovementioned arrangements offer some improvement over the inductive transformer ballasts, they are still rather heavy and require a large number of components. As a result, such arrangements are generally too expensive to be considered at the present time for high-volume mass production. In addition, such arrangements are capable of only low-frequency operation and are susceptible to producing undesirable amounts of rfi noise.

SUMMARY OF THE INVENTION Briefly, in accordance with the present invention, an are discharged lamp control circuit is provided which avoids many of the shortcomings and disadvantages associated with prior art arc discharge lamp control arrangements such as described hereinabove. A control circuit in accordance with the invention includes an input terminal means adapted to receive an ac input voltage signal. An ac input voltage signal received at the input terminal means is converted by a converter means coupled to the input terminal means to a dc voltage signal. The dc voltage signal is applied to a starting means coupled to the converter means which operates in response to the dc voltage signal to produce a control voltage. The control voltage is employed in the control circuit of the invention for initiating operation of an oscillator circuit means.

The oscillator circuit means of the invention generally includes a transistor having a conducting condition and a non-conducting condition, an impedance means coupled to the starting means and to the transistor, and a transformer means coupled to the transistor and to an arc discharge lamp which is to be operated by the control circuit. The impedance means operates in response to the control voltage produced by the starting means to develop a voltage thereacross for initiating operation of the transistor in its conducting condition. When the transistor is initially operating in its conducting condition, the transformer means operates to cause the transistor to operate more fully in its conducting condition. When the transistor is operating more fully in its conducting condition, the transformer means then operates to cause the transistor to operate in its non-conducting condition. While the transistor is successively operating in its conducting and non-conducting conditions, the transformer means further operates to produce an ac operating voltage signal for operating the arc discharge lamp.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates a single-transistor, solid-state ac fluorescent lamp ballast in accordance with the invention; and

FIG. 2 illustrates a modified version of the solid-state ac fluorescent lamp ballast shown in FIG. 1.

GENERAL DESCRIPTION OF THE INVENTION FIG. 1

Referring now to FIG. 1, there is shown a solid-state ac fluorescent lamp ballast I in accordance with the present invention. The ballast 1 includes a pair of input terminals 2 to which an input signal is applied for operating the ballast 1. Typically, the input signal is an ac voltage signal having an amplitude of approximately 1 10-120 volts and a frequency of approximately 50-60 hertz. The input temiinals 2 are connected to a conventional full-wave bridge rectifier circuit 4 employing four diodes d. The output of the full-wave rectifier circuit 4 is applied across a filter capacitor CI, for filtering the full-wave recitifed output of the rectifier circuit 4, and also across a starting circuit 6 comprising a series arrangement of a diode D and a resistor R1. As will be explained hereinafter, the starting circuit 6 serves to initiate operation of a blocking oscillator circuit 7 connected therewith.

The blocking oscillator circuit 7 generally comprises an npn transistor 01, a storage capacitor C2, a bypass capacitor C3, a current-limiting resistor R2, and a lightweight ferrite core air-gap transformer T. The ferrite core air-gap transformer T includes a primary winding P, and a plurality of secondary windings 81-85.

As indicated in FIG. 1, the storage capacitor C2 of the blocking oscillator circuit 7 is connected in parallel with the diode D. The top end of the primary winding P of the air-gap transformer T is connected directly to the collector of the transistor Q1 and the other (bottom) end is connected directly to one end of the resistor R1. The secondary winding S1 of the air-gap transformer T represents a regenerative feedback winding and is connected at one end directly to the base of the transistor Q1 and at the other end to the emitter of the transistor 01 via the current-limiting resistor R2 and the storage capacitor C2. The bypass capacitor C3 is connected between the emitter and collector of the transistor 01 and serves to protect the transistor 01 from any switching transients occurring in the primary winding P of the air-gap transformer T by providing a current path for such transients around the transistor 01.

The secondary winding S2 of the air-gap transformer T represents a step-up load winding for providing an operating voltage (e.g., 400-600 volts ac) for a pair of fluorescent lamps L1 and L2 and is connected in series with the fluorescent lamps L1 and L2 via a ballasting capacitor C4. The ballasting capacitor C4, in conjunction with the inductive leakage reactance of the air-gap transformer T, acts to limit current through the lamps L1 and L2 during operation thereof. The ballasting capacitor C4 also serves to provide a unity power factor load condition. Typically, the fluorescent lamps L1 and L2 are of the rapid-start, 40-watt T12 type. The secondary windings 53-85 of the air-gap transformer T represent filament heating windings for supplying filament voltage to the filaments f of the fluorescent lamps L1 and L2.

OPERATIONFIG. 1

In the operation of the solid-state ac ballast 1 of FIG. 1, an ac voltage signal applied to the input terminals 2 of the ballast l is full-wave rectifed by the full-wave rectifier circuit 4 and applied across the filter capacitor C1. The full-wave rectified voltage is filtered by the filter capacitor C1 to provide a dc voltage across the starting circuit 6. Typically, in the interest of cost, the filter capacitor C1 is selected to have a small value (e.g., 50 microfarads). Therefore, the dc voltage produced by the filter capacitor C1 includes a high ripple content, a condition which is entirely acceptable in the present invention. In response to the dc voltage produced by the filter capacitor C1 across the diode D and the resistor R1, current flows through the resistor RI into the storage capacitor C2. The storage capacitor C2 is gradually charged by this current and when the voltage developed across the storage capacitor C2 reaches the forward-bias voltage of the diode D, typically 0.6-0.7 volts, it is clamped to that value by the diode D. This voltage across the storage capacitor C2 (0.6-0.7 volts) causes the base of the transistor O1 to be biased positive with respect to the emitter and is of sufficient amplitude to establish a small amount of base current in the transistor 01. As a result, a small amount of initial collector current flow is established in the transistor 01 and, thus, through the primary winding P of the air-gap transformer T.

In response to the initial current flow through the primary winding P, a positive voltage is initiated by the airgap transformer T across the load winding S2 for operating the fluorescent lamps L1 and L2. At the same time, a feedback voltage is initiated by the air-gap transformer T in the feedback winding S1 and coupled into the base of the transistor 01. The polarity of the feedback winding 81 is established (as indicated by the conventional dot notation) so as to cause the base of the transistor 01 to become more positive with respect to the emitter (positive feedback), thereby causing increased collector current flow into the primary winding P and, therefore, a consequential increase in the value of the voltage across the load winding S2 and an increase in the value of the feedback voltage induced in the feedback winding S1. The above action involving the transistor Q1 and the feedback winding S1 is regenerative in nature, and continues in a very rapid manner until the transistor Q1 operates in its saturation state. During the abovementioned regeneration action, as the voltage induced in the feedback winding 81 quickly increases in value, the diode D is reverse biased by the voltage induced in the feedback winding S1 (that is, the anode of the diode D becomes negative with respect to the cathode) and the voltage across the storage capacitor C2 is reversed from its previous, initial polarity.

As the transistor O1 is caused to operate near saturation by the voltage induced in the feedback winding 81, current in the primary winding P of the air-gap transformer T increases very little, and the voltage across the load secondary winding S2 and, thus, across the lamps L1 and L2, becomes reduced from its peak positive value and approaches zero value. At the same time, the voltage induced in the feedback winding S1 rapidly decays and, through regenerative action, causes the base drive for the transistor 01 to become rapidly reduced thereby causing the transistor 01 to rapidly operate in its non-conducting state and to provide a minimum value of collector current to the primary winding P. It is to noted that during the abovementioned regeneration action, as the voltage in the feedback winding Sl becomes reduced, the capacitor C2 is charged toward its initial polarity by virtue of current again flowing through the resistor R1. The value of this voltage approaches the value of the forward-bias voltage of the diode D. As current flow in the collector circuit of the transistor ()1 and, therefore, through the primary winding P of the air-gap transformer T, assumes the minimum value, as mentioned hereinabove, the voltage across the load secondary winding S2 increases in the negative direction to its maximum negative value and then back in the positive direction. A feedback voltage is also induced in the feedback winding S1 of the air-gap transformer T having a polarity opposite to that previously induced in the feedback winding 81. This feedback voltage serves momentarily to keep the base of the transistor 01 negative with respect to the emitter and thereby to keep the transistor 01 in its nonconducting state. Although a voltage is present across the storage capacitor C2 at this time tending to make the base of the transistor Q1 positive with respect to the emitter, the combined value of this voltage and the feedback voltage is insufiicient to cause the transistor 01 to operate in its conducting state.

When the storage capacitor C2 is again charged by current flow through the resistor R1 to a value equal to the forward-bias voltage of the diode D (that is, 0.6-0.7 volts), a new cycle of operation of the blocking oscillator circuit 7 commences. With repeated operation of the blocking oscillator circuit 7 through several cycles, high-frequency ac voltage signals (e.g., 20 kilohertz) are caused to be produced across the load secondary winding S2 of the air-gap transformer T for operating the fluorescent lamps L1 and L2 at a high frequency, thereby resulting in improved lamp operating efficiency.

5 MODIFIED BALLAST-FIG. 2

Referring now to FIG. 2, there is shown a solid-state ac ballast l representing a modified version of the ac ballast 1 shown in FIG. 1. As will be apparent hereinafter from a listing of the particular components employed in the ballasts of FIGS. 1 and 2 and from typical values for the parameters of such components, the ballast 10 of FIG. 2 is the same as that of FIG. 1 with the exception that a lightweight ferrite toroid T1 having a square hysteresis loop is employed in the base circuit of the transistor Q1, a different value of resistance is employed for the current-limiting resistor R2, and a dif ferent number of turns is employed for each of the primary winding P, the feedback winding S1, and the load winding S2. As indicated in Fig. 2, the ferrite toroid T1 includes a primary winding PW connected in series with the current-limiting resistor R2 and the feedback winding 81, and a secondary winding SW connected at one end to the base of the transistor Q1 and at the other end to one end of the storage capacitor C2. The ferrite toroid Tl, due to its square hysteresis loop, becomes saturated and unsaturated very quickly and serves more quickly to switch the transistor Q1 between its conducting and non-conducting states. As a result, the possibility of the air-gap transformer T becoming saturated is minimized.

Some typical values for the parameters of the components employed in the ballasts 1 and 10 are as follows:

d IN4UO3 D 1N4003 0| 2N 3902 Cl 50 microfarads C2 0.44 microfarads C3 0.0 l 2 microfarads C4 0022 microfarads R1 68 kilohms R2 (FIG. I) 27 ohms AIR GAP 0.028 inches P 76 turns (FIG. 1); 86 turns (FIG. 2)

S1 (FiG. l) 4 turns 81 (FIG. 2] 7 turns 52 (FIG. I) 120 turns 52 (FIG. 2) I40 turns S3 l lzturns S4 l mums S l'hturns Core (TJ El-40-G P3, Nippon Industrial Ferrite Corp.

Core (Tl) TO62Hl0lA, Allen Bradley Corp.

PW 4l turns SW 37 turns While there has been shown and described what are considered preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as called for in the appended claims.

What is claimed is:

l. A control circuit for operating an arc discharge lamp, comprising:

input terminal means adapted to receive an ac input voltage signal;

converter means coupled to the input tenninal means and operative to convert the ac input voltage signal received at the input terminal means to a dc voltage signal;

starting means coupled to the converter means and operative in response to the dc voltage signal to produce a control voltage; and oscillator circuit means, said oscillator circuit means comprising: a transistor including a base, an emitter and a collector and having a conducting condition and a non-conducting condition; impedance means coupled to the starting means and to the transistor, said impedance means including a capacitance; and transformer means coupled to the transistor and to the arc discharge lamp; said transformer means including a ferrite toroid having a primary winding and a secondary winding, one end of the secondary winding being connected to the base of the transistor and the other end being connected to the emitter of the transistor through the capacitance; and

an air-gap transformer having a primary winding in series with the collector of the translator, a feedback secondary winding having one end thereof connected to one end of the primary winding of the ferrite toroid and the other end thereof connected to the other end of the primary winding of the ferrite toroid, and a load secondary winding coupled to the arc discharge lamp;

said transformer means being operative when the transistor is initially operating in its conducting condition to cause the transistor to operate more fully in its conducting condition and, when the transistor is operating more fully in its conducting condition, to then cause the transistor to operate in its non-conducting condition, said transformer means being further operative while the transistor is successively operating in its conducting and non-conducting conditions to produce an ac operating voltage signal for operating the arc discharge lamp;

said impedance means being operative in response to the control voltage produced by the starting means to develop a voltage thereacross for initiating operation of the transistor in its conducting condition.

2. A control circuit in accordance with claim 1 wherein the arc discharge lamp is a fluorescent lamp.

3. An ac ballast for operating an arc discharge lamp comprising:

input terminal means adapted to receive an ac input voltage signal;

full-wave rectifier means coupled to the input terminal means for rectifying the ac input voltage signal received at the input terminal means;

a filter capacitance coupled to the full-wave rectifier means for filtering the full-wave rectified voltage signal produced by the full-wave rectifier means to produce a dc voltage signal;

a starting circuit connected in parallel with the filter capacitance and comprising a series arrangement of a resistance and a diode; and

an oscillator circuit comprising:

a storage capacitance connected in parallel with the diode;

a transistor having a base, an emitter, and a collector;

a ferrite toroid having a primary winding and a secondary winding, one end of the secondary winding being connected to the base of the transistor and the other end being connected to the emitter of the transistor through the capacitance; and

an air-gap transformer, said air-gap transformer having a primary winding connected between the collector of the transistor and the resistance included in the starting circuit, a regenerative feedback secondary winding having one end thereof connected to one end of the primary 

1. A control circuit for operating an arc discharge lamp, comprising: input terminal means adapted to receive an ac input voltage signal; converter means coupled to the input terminal means and operative to convert the ac input voltage signal received at the input terminal means to a dc voltage signal; starting means coupled to the converter means and operative in response to the dc voltage signal to produce a control voltage; and oscillator circuit means, said oscillator circuit means comprising: a transistor including a base, an emitter and a collector and having a conducting condition and a non-conducting condition; impedance means coupled to the starting means and to the transistor, said impedance means including a capacitance; and transformer means coupled to the transistor and to the arc discharge lamp; said transformer means including a ferrite toroid having a primary winding and a secondary winding, one end of the secondary winding being connected to the base of the transistor and the other end being connected to the emitter of the transistor through the capacitance; and an air-gap transformer having a primary winding in series with the collector of the translator, a feedback secondary winding having one end thereof connected to one end of the primary winding of the ferrite toroid and the other end thereof connected to the other end of the primary winding of the ferrite toroid, and a load secondary winding coupled to the arc discharge lamp; said transformer means being operative when the transistor is initially operating in its conducting condition to cause the transistoR to operate more fully in its conducting condition and, when the transistor is operating more fully in its conducting condition, to then cause the transistor to operate in its non-conducting condition, said transformer means being further operative while the transistor is successively operating in its conducting and non-conducting conditions to produce an ac operating voltage signal for operating the arc discharge lamp; said impedance means being operative in response to the control voltage produced by the starting means to develop a voltage thereacross for initiating operation of the transistor in its conducting condition.
 2. A control circuit in accordance with claim 1 wherein the arc discharge lamp is a fluorescent lamp.
 3. An ac ballast for operating an arc discharge lamp comprising: input terminal means adapted to receive an ac input voltage signal; full-wave rectifier means coupled to the input terminal means for rectifying the ac input voltage signal received at the input terminal means; a filter capacitance coupled to the full-wave rectifier means for filtering the full-wave rectified voltage signal produced by the full-wave rectifier means to produce a dc voltage signal; a starting circuit connected in parallel with the filter capacitance and comprising a series arrangement of a resistance and a diode; and an oscillator circuit comprising: a storage capacitance connected in parallel with the diode; a transistor having a base, an emitter, and a collector; a ferrite toroid having a primary winding and a secondary winding, one end of the secondary winding being connected to the base of the transistor and the other end being connected to the emitter of the transistor through the capacitance; and an air-gap transformer, said air-gap transformer having a primary winding connected between the collector of the transistor and the resistance included in the starting circuit, a regenerative feedback secondary winding having one end thereof connected to one end of the primary winding of the ferrite toroid and the other end thereof connected to the other end of the primary winding of the ferrite toroid, and a load secondary winding adapted to be connected to the arc discharge lamp.
 4. A ballast in accordance with claim 3 further comprising a ballasting capacitance connected in series with the load secondary winding of the air-gap transformer.
 5. A ballast in accordance with claim 4 further comprising a bypass capacitance connected between the collector and the emitter of the transistor. 